Cut off top of pumpkin to make a lid. Remove the seeds and scrape out any stringy pulp. Combine brown rice, bread, onion, celery, apples, chestnuts or cashews, and herbs in a large mixing bowl and mix well with hands. Add stock and butter, and mix well, adding soy sauce and salt if desired. Stuffing should be moist but not wet. Pack loosely into pumpkin, replace lid, and bake on oiled cookie sheet for 1-1/2 hours or more at 325 degrees F. It is done when a fork pushes easily through the pumpkin. Transfer to a casserole dish and serve at the table, scooping out some of the tender pumpkin flesh with each serving of stuffing. You may eat the skin too. (If you have too much stuffing for your pumpkin, place extra in an oiled casserole, cover, and bake for 1 hour.)